Transformers are used extensively in electrical and electronic applications. Transformers are useful to step voltages up or down, to couple signal energy from one stage to another, and for impedance matching. Transformers are also useful for sensing current and powering electronic trip units for circuit interrupters such as circuit breakers and other electrical distribution devices. Generally, the transformer is used to transfer electric energy from one circuit to another circuit using magnetic induction.
A transformer includes two or more multi-turned coils of wire placed in close proximity to cause a magnetic field of one coil to link to a magnetic field of the other coil. Most transformers have a primary winding and a secondary winding. By varying the number of turns contained in the primary winding with respect to the number of turns contained in the secondary winding, the output voltage of the transformer can be easily increased or decreased.
The magnetic field generated by the current in the primary coil or winding may be greatly concentrated by providing a core of magnetic material on which the primary and secondary coils are wound. This increases the inductance of the primary and secondary coils so that a smaller number of turns may be used. A closed core having a continuous magnetic path also ensures that practically all of the magnetic field established by the current in the primary coil will be induced in the secondary coil.
When an alternating voltage is applied to the primary winding, an alternating current flows, limited in value by the inductance of the winding. This magnetizing current produces an alternating magnetomotive force which creates an alternating magnetic flux. The flux is constrained within the magnetic core of the transformer and induces voltage in the linked secondary winding, which, if it is connected to an electrical load, produces an alternating current. This secondary load current then produces its own magnetomotive force and creates a further alternating flux which links back with the primary winding. A load current then flows in the primary winding of sufficient magnitude to balance the magnetomotive force produced by the secondary load current. Thus, the primary winding carries both magnetizing and load current, the secondary winding carries load current, and the magnetic core carries only the flux produced by the magnetizing current.
In producing a primary winding for a transformer, conventionally, a winding mandrel winds a conductor wire around a secondary winding on the transformer core. This produces a formation of primary voltage coils on the transformer core. Typically, the conductor wire of the primary winding comprises an insulated wire having a flat cross section. In conventional transformers, the primary winding is wound around the transformer core in a helical manner, proceeding back and forth about each end of the transformer core. Each helical layer rests entirely upon the next layer closer to the transformer core because each subsequent helical layer extends the same length as all prior layers. This provides for a relatively poor conductor space factor within the core window. Additionally, the close proximity of the various layers of conductor wires does not assist in preventing arcing between the layers.
Accordingly, a transformer core in accordance with the present invention provides an inexpensive and simple solution to eliminate the drawbacks of the prior transformer windings.